1. Field of the Invention
This invention provides an improved separator for alkaline storage batteries intended for use in spacecraft applications. Separators intended for use in alkaline storage batteries for spacecraft power systems must frequently operate in an electrolyte starved condition, must be gas permeable, must exhibit good mechanical strength and must be chemically and thermally stable. Composites are employed in the fabrication of separators because of their potential for achieving an optimum set of operating characteristics such as those set forth above. Therefore, this invention describes an optimum composite and the process for making it from known materials.
2. Description of the Prior Art
There are many approaches to the solution of the problem of preparing composite separators for use in alkaline storage cells. Typical examples of these approaches are disclosed in: the teachings of A. Langer et al in U.S. Pat. No. 3,749,604 for Heat Resistant Substrates and Batteries Separators Made therefrom; the teachings of Fank C. Arrance in U.S. Pat. No. 3,861,963 for Battery Separator Construction; the teachings of Nigel I. Palmer in U.S. Pat. No. 3,933,525 for Battery Separator Manufacturing Process; the teachings of Joseph A. Cogliano in U.S. Pat. No. 4,110,143 for Process for Making a Wettable Polypropylene Battery Separator; and the teachings of Phillip Bersting in U.S. Pat. No. 4,122,133, for Material for an Alkaline Cell Separator and Process of Making.
Many of the above mentioned teachings have yielded separators which meet with a measure of success. However, this art has not totally satisfied the requirements for alkaline storage cells to be used in certain spacecraft applications. Generally, the separators of the prior art are either non-wettable, chemically unstable, thermally unstable or gas impermeable, or a combination of the latter.
As far as it is known to applicant, the closest prior art to the present invention is that disclosed in applicant's copending application Ser. No. 948,119 identified above. In application Ser. No. 948,119, applicant and his coinventors described a process for reinforcing structually fragile inorganic fabrics with organic polymers. This approach was taken in order to utilize the electrolytic retention and wettability characteristics of inorganic fabrics which, in and of themselves, were unsuitable for use as separators in alkaline storage cells. The fabric reinforcing technique described in application Ser. No. 948,119, has as its major limitation the ability to apply sufficient reinforcing material to the inorganic fabric to achieve the strength objectives without losing the wettability characteristics of the inorganic material.
While each of the separators prepared in accordance with the teachings of the above prior art can be classified as composites prepared from individually old materials, these separators contain certain structural and/or material distinctions which tend to limit their utility for spacecraft applications. Therefore, there is a need for a composite separator material which exhibits all of the above stated desirable characteristics and none of the disadvantages of the prior art separators.